System of control



R. E. HELLM-UND. SYSTEM OF- CONTROL.

APPLICATION FILEQ APR. 18, 1917.

Patented Nov. 16, 1920.

3 SHEETS-SHEET I- INVENTOR WITNESSES:

M623 7 ATTORNEY mm Nov. 16, 1920.

3 SHEETS-SHEET 2.

R. E. HELLMUND.

SYSTEM OF CONTROL.

APPLICATION FILED APR.I8,1911- 1,358,735.

ATTORNEY R. E. HELLMUND.

,SYSTEM OF CONTROL.

APPLICATION FILED APR. 18, I917- 1 ,35s,73'5, Patented Nov. 16, 1920.

3 SHEETSSHEET 3.

WITNESSES; INVENTdR Rudolf 5. He llmufld BY WW ATTORNEY res PATENTGFFICE.

RUDOLF E. HELLMUND, F SWISSVALE, PENNSYLVANIA, ASSIGNOR TO WESTING HOUSEELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENN- SYLVANIA.

SYSTEM OF CONTROL.

Application filed April 18,

' To all whom it may concern: 7

Be it known that I, RUDOLEE. HELLMUND, a subject of the Emperor ofGermany, and a resident of Swissvale, in "the count of Allegheny andState of Pennsylvania, ave inventeda new and useful Improvement inSystems of Control, of which the following is a specification.

My invention relates to systems of control and especially to systemsembod ing a plurality of induction motors or ot er driving unitsforhauling a common load.

One difficulty in operating a locomotive propelled by a plurality ofinduction motors or other driving units consists in maintaining an evendistribution of electricalload among the several motors, underaccelerating or regenerating conditions, and, at the same'time, alsopreventing the occurrence of a general overloadupon the locomotive.farious presumptive load-halancing arrangen'rents of-th'e prior art tendto aggravate the difiiculty. when one set of locomotive wheels begins tofslipf whereb the load on the corresponding motor is re need and theremaining motors'are more heavily loaded.

The object oi my present invention is to provide, in a system of theabove-indicated character, means for automatically fixing or adjustingthe total load upon a lurality of driving units and other means iorautomatically and independently balancing the .load distribution betweenthe several units,

irrespective of total load conditions;

More specifically stated, it is one object of my invention to provide arelay device for automaticall counter-balancing the to tal driving-unitoad against a selected value of supply-circuit voltage and other relaydevices for counterbalancing the individual driving-unit load againstthe proportionate motor load, whereby each driving unit continuouslyperforms-the intended share of work.

My invention may best be understood by reference to the; accompanyindrawings, wherein Figure 1 is a simpllfie elevational view of a two-unitlocomotive-embodying a system of my present invention; is a diagrammaticview of the main or es-- sential circuit connections to be employed inaccordance with one form of my invention;

- Fig. 3 is a diagrammatic view of a portion of an auxiliary governingsystem for mashown as liquid rheostats Fig. 2

1917. Serial No. 1 2,901.

niplating certain circuits that are shown in Fig. 2; Fig. 4 and Fig. 5are diagrammatic views, corresponding, respectively, to Fig. 2 and Fig.3, of a modification of the present invention; and Fi 6 is an enlargeddiagrammatic view, chie y in section, of portions of the governingapparatus that is illustrated in Fig. 2.

Referring to Fig. 1 of the drawings, the locomotive illustratedcomprises two similar half-units 1 and 2 which are respectively providedwith pairs of driving induction motors -M1 and M2, and M3 and M4, and

Specification of Letters Patent. Patented N 16 192Q apair of articulatedtrucks 3 and 4 each of which is provided with any suitable type ofdriving mechanism 5 for transmitting the mechanical energy of thecorresponding driving motor to the associated vehicle wheels. While Ihave shown four electric motors located upon as many trucks in adouble-unit locomotive, it will be understood that .any other number ortype of driving units may readily be utilized in connection with mypresent invention.

The system shown in Fig. 2 comprises a plurality of main three-phasesupplycircuit conductors 10, 11 and 12; a plurality of auxiliarytrain-line conductors 13, 1% and 15 and of main bus-bar or train-lineconductors 1,6, 17 and 18; a plurality oi the driving units M1 to M4,inclusive, this case constituting induction motors respechavingthree-phase primary stator tivelly -win ings P1, P2, P3 and P4 andsecondary rotorwindings S1, S2, S 3 and S4; a plurality of.resistance-varymgl devices, here vided with an operating mechanism 20for varying the secondar -circuit resistance of the corresponding inuction motor; a pin rality of limit switches L1 to L4, inclusive, of a.familiar type, that are associated withthe respective primary motorwindings for a purpose to be set forth; a line switch 21 of any suitablety e; a master controller or regulator 22 of t e well-knowninductionregulator type; a master relay device com-. prising aninduction motor 23 that is energized from the master controller 22 and amechanically duction motor 24 that is energized from the main motors, ashereinafter set'forth in de-' tail; a plurality of other relay devicesto 28, inclusive, that are electrically associated with the severalmotors and operatoined oppositely acting in- 1 R1, etc., proin a mannerto be set forth.

; flows through the hollow valve to the ing me -hanisms therefor, forthe purpose of individually balancin the motor loads, as subse uentlydescribe and a plurality of trans ormers 29, 30 and 31 that areassociated with the last-mentioned relay devices and also with themaster-relay device,

lit will be understood that the main sup ply-circuit conductors l0, 11

as a three-phase transmission line or a single-phase transmission line,in conjunction with a phase converter of a familiar type.

l or the sake of simplicity and clearness, only a single liquid rheostatLR]. and its operating mechanism 20 are illustrated in Fig. 2, but itwill be understood that corresponding apparatus is: actually associatedwith each of the secondary induction motor windgs S1 to S4, inclusive,in the system of Fig. 2 and also in the'subsequently described system ofFig. 4i. i

The main supply-circuit conductors 12, 11 and 10 are respectivelyconnected, through the primary windings 40, 41 and 42 of thetransformers 29, 30 and 31, to the main bus-bars 16, 17 and 18, whencecircuit is completed to the terminals of the primary induction-motorwindings, through conductors 43, 4d and 45', respectively.

The terminals of each secondary induction-motor winding, such as windinS1, are connected through conductors 46, 4 and 4:8 to the respectiveelectrodes 49 of the liquid rheostat LE1, which is illustrated on alarger scale in Fi 6. The valve and the operating mechanism are shown intheir uppermost and active positions in Fig. 1 and in their lowermost ornormal positionsin Fig. 6. The rheostat may be of any famillar type andis here shown as comprising a mainwith which is associated a movablehollow and 12 ma be energized from any suitable source, suc

valve 58 for the purpose of determining. the

liquid level in the'electrode-containing compartment; an inlet 59 to thetank and an outlet 60 from the reservoir 56, a continuous circulation ofelectrolyte preferably being maintained through the agency of a sultablepump (not shown), for example.

The rheostat valve 58 is provided with an upper cylindrical portion 61of smaller diameter'than the surrounding opening 57,

whereby the initial flow of electrolyte from the inlet passes throughthe opening 57 around the valve 58 to the reservoir 56. As soon as thelower cylindrical portion 62, which has a diameter substantially equalto that of the tank openin 57, is raised into engagement with the Si esof the opening,

the liquid level in the tank' 55 immediately rises to the top'of thevalve 58 and verthe al ied voir 56. Thus, by raising and lowering theyalve 58 through the agency of the operatlng mechanism 20, as about tobe described,

the liquid level in the electrode-containing compartment iscorrespondingly varied,

whereb' the secondary-circuit resistance of induction motor is likewisechanged to produce suitable accelerating or re enerative conditions inthe motor.

he operatin mechanism 20 is of a familiar electrical y-controlled,pneumaticallyactuated type and comprises a pinion 63 that is-rig1dlysecured to a pulley shaft 6% which is attached to the rheostat valve 58by a suitable rope or cable 65. The pinion 63 meshes with a verticallymovable rack member 66, the opposite ends of which con stitute pistons67 and 68 that travel within nism just described, without regard to thethereby may electrical connection effected be set forth as follo, s:Since the va ve 72 is normally open to admit fluid pressure to thecylinder 70, the mechanism is normally biased to the illustratedosition, which corresponds to the inoperative condition or" the liquidrheostat. 'Upon concurrent ener 'zation of the actuating coils 0nl and Ul, fluid-pressure condltions in the mechanism are reversed, that is, thecylinder 69 and 1s exhausted from the other cylinder 70, whereby anupward movement of the pistons 67 and'68 ensues. To arrest such movementat any time, it is merely necessary to deenergize the @ff-l coil,whereupon fluid-pressure conditions in the apparatusare immediatelybalanced to effect a positive and reliable stoppage of the mechanism.

To produce fa return movement of the operating device, the actuatingcoils are both deenergized, whereby fluid pressure conditions revert tothe original unbalanced state, and the desired movement is effected;

As previously stated, the other unillustrated'. liquid rheostats arealso provided with similar operating mechanisms, and, to distinguish thevarious actuating coils, such coils have been designated in Fig. 3 asOn-2, Ofi'2, Qn'--3, Ofi3, and Oil-d and Ofi t, the. numeralscorrespondin to those employed-Zindenoting the severe in duction motorsto Mt, inclusive.

pressure isadmitted to llltl its It will be understood that variousnecessary circuit switches have been omitted from Fig. 2 in order torender the illustration as simple, and clear as possible, and only thecircuit connections that are essential in the employment of my presentinvention are shown. 7

The line switch 21 is provided with a plurality of blades 80 forconnecting the master controller 22 to the supply-circuit conductors 10,11 and '12, and an auxiliary switch blade 81 that is utilized for aurpose to be described in connection with ig. 3 is also mechanicallyassociated with the operating handle 820i the switch.

The master controller or induction regulator 22 may be ofany well-knownty e and is here shown as comprising a plura it of stationary primarycoils 83, 84 and 85, w ich are connected to the respective blades of theline switch 21, and a movable wound rotor 86, the position of which mabe adjusted by means of an operating han le 87 v The primary winding 90of the auxiliary induction motor 23, comprising a part of the masterrelay device, has its three-phase windings respectivel connected inseries relation with the primary stator windings 83, 84 and 85 of theinduction regulator 22,

and a suitable rotor winding 91 for the induction motor 23 is mountedupon a shaft 92 which also carries a differentially-enerized andoppositely-acting rotor 93 of the induction motor 24, the three-phaseprimary winding 94 of which is connected to the auxiliary train-lineconductors 13, 14 and 15. The master relay device shaft 92 also carriesan auxiliary drum 95, upon which is mounted a contact segment 96 thatcomletes an auxiliar circuit, to be described in connection wit Fig. 3,when the relay device occupies a certain position. 'For the purpose ofnormally maintaining the relay device in the middle position shown, aplurality of suitable centerin springs 97 and 98 or the like, areattache to the shaft 92. The relay devices 25 to 28, inclusive, areidentical and, consequently, only the device 25 need be described indetail. The rela device 25 com rises a primary stator win ing 105 thatis connected to the auxiliary train-line conductors 13, 14 and 15 and asquirrel-cage rotor 106 having a supporting shaft 107 upon which is alsomounted a second squirrel-cage rotor 108 thatis differentially energizedfrom a primary'stator winding 109 to oppose the action of the rotor 106.A plurality of series trans former windings 110, 111, and 112 are cons.

nected in series relation with the respective phase windings 109, suchseries transformers being energized in accordance with the currentstraversing the primary stator windings of the mam induction motor M1,whereby the torque exerted by the squii'relwinding 86 cage rotor 108 isproportional to the current in the main-motor windingsa A small drumcontroller 113, or its equivalent, is also carried by the relay deviceshaft 107 to effect the insertion of a contact member 114 in a certainauxiliary circuit, as described in connection with Fig. 3, when therelay device occupies the position shown. The centering sprin 97 and 98are also again preferably provi ed.

The remaining relay devices 26,27 and 28 are similarly connected incircuit relative to the other main motors and are respectively providedwith auxiliary contact mem bers 115, 116 and 117 for performin functionssimilar to that of contact mem er 114 of the relay device 25. Theauxiliary trainline conductors 13, 14 and 15 are energized from thestar-connected secondary windings 120, 121 and 122 of the supplyc1rcuit-energized transformers 29, 31 and 30, respectively. Each of thesecondary transformer windings is provided with a movable tap 123, allof the taps being connected throu h a common conductor 124 for a purposeto %e set forth.

it will be seen that, by reason of the recited arrangement of circuits,the voltage impressed upon the terminals of the primary winding 90 ofthe induction motor 23, constituting a part of the master relay device,may be varied at will with respect to the supply-circuit voltage bymanipulating the operating handle 87 for the secondary of the mastercontroller or induction regulator 22. On the other hand, the voltageimpressed upon the primary winding 94 of the induction motor 24,comprising the remaining part of the master relay device, isproportional to, and varies with, the total load or sum of the averageloads upon the several driving units or induction motors M1 to M4,inclusive. By suitably adjusting the master controller 22, the totalmotor load, thus pre-selected, may be thenceforth automatical ymaintained by the action of the master relay device, by causing thelatter to simultaneously govern all of the liquid rheostats LE1 etc. orother resistance-varying devices. Thus, if the total motor load tends toincrease, for any reason, the torque of the auxiliary induction motor 24overcomes that of the opposing supply-circuit-energized induction motor23 to actuate the rela device into such a position that all of t eliquid-rheostat-operating mechanisms '20 are caused to lower the liquidlevel in the respective rheostats and thus reduce the total motor loadto the desired values. On the contrary, if the total motor load tends todecrease, the torque of :the induction motor 23 predominates to actuatethe master-relay deviceintosuch a ting mechanisms are caused to increasethe liquid level in the corresponding rheostats and thus increase thetotal motor load. In the intermediate position illustrated, the

. mary windings of the correspon ing main &5

opposing motor torques substantially counter-balance each other, and thevarious liquid rheostats aremaintained in whatever position they happento occupy, since only the corresponding Ofi' coils are deenergized, aspreviously explained.

A similar action occurs in connection with the individual relay devices25 to 28, inelusive. In each instance, a voltage corresponding to thetotal motor load and, therefore, to the proportionate load upon eachmotor, namely, one quarter of the combined load, in the present case, isimpressed upon the windings of one of the induction motors constitutingthe relay device 25, for example, while a voltage corresponding to theactual motor current traversing the primary windings P1, etc. isimpressed upon the correspondin primary winding 109 of the allied relaydevices 25, etc. Thus, the proportionate or evenly-balanced motor loadproduces a torque upon the squirrelcage rotor 106 that is opposed by thetorque exerted by the squirrel-cage rotor 108, which is energized inaccordance with the actual current traversing the corresponding mainmotor.

Consequently, under conditions of an even distribution of load betweenthe several motors, the contact members 114 to 117,

inclusive, of the respective individual relay devices 25, 26, 27 and 28remain in the illustrated position to allow movement of the correspondinoperating mechanism 20 to gradually re uce the secondary-circuitresistance of the allied motor, but, whenever the actual currenttraversin the primotor increases above the above-mentioned proportionatevalue, the torque exerted by the squirrel-cage rotor 108 predominatesand actuates the relay device 25, etc. into such position that thecorresponding operating mechanism is caused to increase. thesecondary-circuit resistance of the overloaded main motor and thusquickly bring about evenly-balanced load conditions. The remainingindividual relaydevices 26, 27 and 28 act in a similar capacity withreweet to the induction motors M2, M3 and Met.

The function of the movable taps123 for the various transformers 29, 30and 31 is to allow a suitable adjustment of the volt ages between theauxiliary train-line conductors 13, 14 and 15 in case any main motor iscut out from circuit by reason of mi ury.

trated motors should "be rendered inoperative, the transformer taps 123should .be

actuated to .vary the voltage impressed upon the auxiliary train-lineconductors 13,

For instance, ifone of the illusif the contact segment 96 occupies itsopen position Z, all of the actuating coils 14; and 15 to such a degreethat the subsequent total load which it is desired to automaticallymaintain u on the remaining three motors will be 0 a suitable value toact in conjunction with the various-relay devices to efi'ect. aremaining motor circuits, either separately or concurrently.

Referring to'Fig. 3, the auxiliary system shown comprises the variousliquid-rheostat-governing coils On'1 to -Ofi4i, incluproper regulationof the sive, the contact members 96 and 114: to

117, inclusive which are respectively associated withthe master relaydevice and the individual relay devices 25 to 28, inclusive; theauxiliary contact members of the several limit switches L1 to L4,inclusive;

the auxiliary switch blade 81 of the line switch 21; and a battery 13 orother suitable source of energy for exciting the various actuatingcoils.

Assuming that the line switch 21 occupies the illustrated closedposition, the auxiliary circuit is completed from the positive terminalof the battery B through conductor 130, auxiliary switch blade 81' orthe line switch 21, conductor 131, contact member 96 of the master relaydevice, when in its circuit-completing position 0, and conductor 134,where the circuit divides, the

branchv corresponding to the induction mo tor M 1 including contactsegment 117 of the relay device 28, when in its closed position,actuating coil @n-l and conductor 135 to a junction-point 136. Anothercircuit includes the contact member 96, and

Iitlll conductor 132, where the circuit divides,

occupies the described position r, the com-j its mon energizing circuitfor the several" liquid-rheostat governing coils is closed,

and the operation of therh'eo'stats is dependent u on the individualcontrolling enever the contact segmentcircuits.

96 occupies its mid-position h, the various Off coils are deenergizedand, consequently, the several. liquid rheostats will remain in whateverposition they happen to occupy unless the individual governing circuitseffect different operation. Finall .Y

for, the several liquid rheostats are simultae a-7st of the variouserating mechanisms are simultaneously e ected to immediately reduce theload upon all of the motors until the master relay device again actuatesthe contact segment 96 into either its intermediate or itscircuit-closing position.

Likewise, whenever the contact segment 117, for example, interrupts thecircuits including conductors 132 and 134 by reason of thepreviously-described operation of the relay device 28, the actuatingcoils Orr-4 and Dil -4: are simultaneously deenergized to produce abackward movement of the corresponding liquid-rheos'tat mechanism and,therefore, a reduction of the corresponding motor load. The function ofthe limit switch Lei, for instance,

is the usual one of interrupting the circuit of the coil Oil-4 and thuscausing the allied liquid rheostat to hold a certain position until thecorresponding motor current has decreased to the desired value.

It will be appreciated that, it desired, the master controller orinduction regulator 22 may be so designed that its maximum deliveredvoltage corresponds to the maximum permissible total current inthe-induction motors, whereby, under such con ditions, the master relaydevice will operate to simultaneously reduce the motor loads in themanner previously described, and the use of limit switches L1 to L4 maythus be eliminated, if deemed advisalole.

Reference may now be had to Fig. 1, wherein the system shown comprisesthe main supply-circuit conductors 10, 11 and 12; the main bus-bars 16,17 and 18; the induction motors or other driving units M1 to M l,inclusive; conductors 150, 151 and 152 for connecting the supply-circuitconductors 10, 11 and 12 to the main bus-bars 17, 18 and 16,respectively, a primary Winding 153 of a transformer being included inthe conductor 151; a plurality of motortype relay devices 155, 156, 157and 158; a master controller or regulator 160 for connecting variableamounts or a supplycircuit-energized transformer winding 161 in circuit;and an inductive or impedance device 162, such as an iron-core inducti ncoil for modifying certain phase relations the various relay devices.

The relay devices are associated with the respective motors forseparately balancing the loads thereof and, inasmuch as the de vices areidentical, only the relay 155 need be described, it comprises acommutatortype armature .165, a main field winding 166 and an auxiliaryfield winding 16? that are wound to produce excitation of the arma ture165 in difi'erentdirections, as indicated by the non-parallelism of theillustrated windings. A secondary winding 168 of a transformer 169having its primary winding 170 connected in circuit with the maininduction motor M1, is connected across-the Zmain field winding 166,whereby the armature 165 is normal energized in accordance with thecurrent traversing the main induction motor M1. The shaft 171 of thearmature 165 also carries a small drumcontroller 172, upon which ismounted a contact segment 173 for governing the actuating coils On--1and Off-4 of the corresponding liquid rheostat (not shown). Thecentering springs 97 and 98 are also preferably provided.

.The auxiliary field winding 167 is connected, through the main fieldwinding 166, across a'proportionate part 180 (in this case, one quarter,since there are four motors) of the secondary winding of thetotal-current-energized transformer 154. The connection and arrangementof parts are such that the voltages of the secondary windin 168 of thesingle-inotor-current-energized transformer 169 and of the proportionatepart 180 of the total-current-energized transformer 154: normallyneutralize each other with respect to the auxiliary" field winding 167that is to say, under conditions of even distribution of load betweenthe four motors, the voltages in question counteract each other and theauxiliary field winding 167 produces no efject.

vvhenever the load in the corresponding motor increases above theproportionate value, however, the auxiliary relay armature 165' isenergized from the auxiliary field winding 16?, as Well as from the mainfield winding 166, and the total effect of such,

field-Winding energizations, together with the phase-modifyin action ofthe inductive device 162, causes tie relay device 155, for example, tomove into a position wherein the contact segment 173 opens the circuitgoverned thereby 'and causes the operating mechanism for thecorresponding liquid rheostat to reduce the motor load and thus restorenormal or evenl balanced load-distribution conditions. correspondingaction occurs through the agency of the remaining relay devices 156, 15?and 158 whenever the corresponding motor load tends to increase abovethe proportionate value, since the field windings correspond ing to theauxiliary field winding 16'? oil the relay device 155 are associatedwith secondary windings of series forme s P'- 1 u A M M l 16 a, 1.78 a17s that are ener ized by the currents traversing the man tors M3 and Mrespectively, an parts 181, and 188, eacn equ part 180' of the secondarywindir c -totel-current-energized transr ormer are 175 and 176,corresponding to the contact members 173 of the relay device 155, areprovided upon the relay devices 156, 157 and 158, respectively.

There lating transformer 161 is provided wit a plurality of taps 185which are successively engaged by a movable contact v movable contactmember 186 of the master till controller, conductor 187, the inductiveor impedance device 162, the: series-related armatures of the relays158, 157, 156 and 155, train-line conductor 17 and conductor 150 to asecond supply-circuit conductor 10.

Assumin that the auxiliary field windings 167 o the various relaydevices 155 to 158, inclusive, are inoperative, by reason of theabove-described equal distribution of motor loads, the automaticmaintenance of a substantially constant total motor current is effectedas follows: Whenever the product of the currents traversing the mainfield windings 166 of the various relay devices and the armatures 165thereof attains a predetermined value, the torque roduced serves torotate the contact mem ers 173, 171, 175 and 176 of the several relaydevices into open-circuit positions, whereby the corresponding liquidrheostat governin coils are denergized to produce backwar movement ofthe liquid rheostat and thus decrease the total motorload. Consequently,the total motor current may be automatically maintained at any valuedependent upon the previous manual adjustment of the master controller160.

llhe separate control of the individual liquid rheostats toautomatically maintain an even distribution of load among the severalmotors has already been described. In this connection, the auxiliaryfield windings 167 of the relay devices should exert a relativelypowerful eilect, as compared with the main field windin. 166, wherebyeven a slight unhalancing or the motor load is suflicient to cause therelay oi the overloaded motor to act. 1

Referring to the auxiliary circuits of Fig. 5, the governing systempartially shown comprises the various actuating coils N-1 to (Jil 1,inclusive,-the contact segments 173 to 176, inclusive, of the relaydevices 155 to 158, inclusive; the contact memhers of the various limitswitches L1 to L1, inclusive; a portion of the master controller 160;and a battery B or other suitable source oi energy.

Assuming that the master controller 160 occupies any operative position,as illustra'ted 41, an. auxiliary circuit is estahlished trom thepositive terminal of the battery B through conductor 195, contactsegment 188 and auxiliary movable contact member 189 of the mastercontroller, and conductor 196 to junction-point 197, where the circuitdivides, one branch including conductor 198 and a second junction-point195 where the circuit further divides, one

device 155, when in its cirhuit-closingposi-- tion, and conductors 204and 205 to the ne ative battery terminal.

imilar circuits, which need not be traced here, are completed for theother liquidrheostat-o crating mechanisms. The limit switches J1 to L4,inclusive, perform functions similar to those described in connectionwith Fig. 3.

It will be observed that, whenever any one of the contact segments 173to 176, inclusive, is actuated to interrupt the circuit governedthereby, the actuating coils of the corresponding. liquid rheostat areboth deenergized, and a return movement of the operating mechanismoccurs to effect a redetermined decrease of the correspon ing motorcurrent.

It should be observed that an important advantage of the above-describedsystems over the prior art systems of which I have knowledge resides inthe fact that the individual motor loads are automatically balanced atall times, irrespective of the total motor load. In other words, theregulating action of the individual motor relays is independent of thesetting or action of the master relay device. For example when alight-Weight train has reached full speed, the combined load may be lessthan that correspondin to the setting of the master rclay, but t eindividual relays fulfil their intended regulating function just as wellas 4 during the accelerating period, since the proper proportionatevalue or" the total. load,

of whatever amount, is counterbalanced against the actual load in eachmotor, as previously described in detail.

In order to prevent slippage conditions or any set of vehicle whee s andor the corresponding motor some form of automatic device dependent, forexample, upon the slip frequency or the sccondary windings of themotors, should be employed.

For this purpose, ll preferably employ one of the systemsset forth in myco-pending application, Serial No. 70,137, filed January 5, 1916.. Bythe use oi such a all preventing in combination the present invention,the desired automatic cific circuit connections or arrangement of partsherein set forth, as various modifications thereof may be effectedwithout departing from the spirit and scope of my invention. I desire,therefore, that only such limitations shall be imposed as are indicatedin the appended claims.

I claim as my invention:

1. In a system of control, the combination with a supply circuit, of apluralit of driving units energized therefrom to aul a common load, anda relay device having actuatin members opposingly energized from saidsupply circuit and said driving units for adjusting the total load uponsaid units.

2. In a system of control, the combination with a supply circuit, of aplurality of driving units ener 'zed therefrom to haul a common load, ana relay device embodying mechanically-joined actuating motors opposinglyenergizedfrom said supply circuit and said driving units for fixing thetotal'electrical load upon said units.

3. In a system of control, the combination with a supply circuit, of aplurality of driving units energized therefrom to haul a common load,means for manually fixing the total load upon said units, and a relaydevice embodying mechanically-joined actuating motors opposinglyenergized from said supply circuit and said driving units forautomatically maintaining said manuaiiy fixed load.

a. a system of control, the combination with a supply circuit, of aplurality oi driving induction motors energized therefrom to haul acommon load and each havv ing a primary and a secondary winding,individuai means for varying the resistance of the severalsecondary-winding circuits, means actin in accordance with predeter=mined relative supply-circuit and motor conditions for controllin all ofsaid individual means to determine the total electrical. ioad upon saidmotors, and means as= I sociated with said last means for separatelycontronlng said individual means to evenly 55315321 38 the load betweenthe several inca system of control, the combination a supply circuit, ofa plurality of driv duction motors energized therefrom I a common loadand each having t and a secondary winding, ind ividis for varying theresistance or the several secondary winding circuits, meansiiierentiailyenergized by predetermined suppiy-c rcuit and driving-unitconditions main motors, and other relay devices each for controlling allof said individual means to adjust the total load upon said/motors, andmeans electrically associated with said last means for separatelycontrolling said individual means to evenly distribute the load betweenthe several motors.

6. In a system of control, the combination with a supply circuit, ofa'plurality of main induction motors ener 'zed therefrom to haul acommon load an each having a primary and a secondary winding, individualmeans for varying the resistance of the several secondary-windincircuits, a master relay device embodying mechanicallyomed actuatingmotors 'opposingly energlzed from said supply circuit and said mainmotors for controlling all of said individual means to fix the totalload, upon said main motors, and other relay devices associated with therespective main motors and each comprising actuating members opposinglyenergized from certain circuits of the respective main motors and from.certain circuits of said master-relay device for separately controllingsaid individual means to balance the load between the several mainmotors.

7. In a system of control, the combination with a supply circuit, of aplurality of main induction motors energized therefrom to haul a commonload and each having a primary and a secondary winding, individual meansfor varying the resistance of the several secondary-winding circuits, amaster relay device embodying mechanically-joined actuating motorsopoosingly energized from said supply circuit and said main motors forcontrolling all of said individual means to fix the total load upon saidcomprising mechanicallyjoined actuating motors opposinglyenergized inaccordance with the proportionate main-motor current and thecorresponding actual main-motor current for separately controlling saidindividual means to balance the load between the several main motors, 8.In a system of control, the combination with a supply circuit, of aplurality of driving' induction motors energized. thereirom to bani acommon load and each having primary and a secondary winding, vidualmeans for varying the resistance of the several secondarywvinding cimeans for pro-selecting the total el load upon the motors, means energiaaccordance with maaically maintain means associated with s separatelycontroll ng said. indi to evenly automaticaliy distribute load betweenthe severai motors, p

9, In a system of control, the combination 186 with a supply circuit, ofa plurality of drivmg induction motors energized therefrom I to haul acommon load and each having a primary and a secondary winding,individual mansfor varying the resistance 'of the severalsecondary-winding circuits,

means for manually fixing the total load upon said motors, a masterrelay device embodyin'g mechanically-joined actuating mo-' torsopposingly energized from said supply circuit and said driving motorsfor controlling all of said individual means to automatically maintainsaid fixed load, and other relay devices each comprisingmechanically-joined actuating motors opposingly energized in accordancewith the proportionate driving-motor current and the correspondingactual driving-motor current for separately controlling said individualmeans to automatically balance the load between the several drivingmotors.

. 10. In'a system of control, the combination with a'supply circuit, ofa plurality of main induction motors energized therefrom 25 to haul acommon load and each having a primary and a secondary winding,individual means for varying the resistance of the severalsecondary-winding circuits, a master rela device embodyingmechanicallyjoine actuating motors opposingly energized from said supplycircuit and-said main motors; for controlling all of said individualmeans, other relay devices each 1 comprising mechanicallyjoinedactuating d ll motors opposingly energized in accordance with theproportionate main-motor current and v the corresponding actualmain-motor current, and an induction regulator for adusting the voltageapplied from the supplycircuit to .said master relay device.

11. In a system of control, the combination with a supply circuit, of aplurality of dynamomlectnc machines energized therefrom to haul a commonload, individual 45,

means for varying the load conditions of the respective machines, meansacting'in accordance with predetermined relative supply-circuit andmachine conditions for controlling all'of said individual means todetermine the total'machine load, and means for independentlycontrolling said individual means to 'halance the machine loadsirrespective off total-load .jconditions.

ld 'lln a system of control, the comhina tion. with a supply circuit,oil a plurality of motors energized therefrom to haul a common load,individual means for ramfing tne'load' conditions of the respectivemachines, a master relay device acting in ac. cordance withpredetermined relative sup ply-circuit-and machine conditions forcontrolling elicit eaidindividual means to dereeeree termine the totalmotor load, and independent relay devices for controlling saidindividual means to evenly distribute the motor loads irrespective oftotal-load conditions.

13. In a system of control, the combination with a supply circuit, of apluralit of driving units energized therefrom to aul a common load,relay means acting in accordance with predetermined relat1ve sup-'-circuit and driving-unit conditions for pl adii usting the total load,and inde endent' means for maintaining balanced loa conditions betweenthe several drivin units.

14. In a system of control, t e combination with a supply circuit, of aplurality of driving units'energized therefrom to haul a 1 common load,means for automatically adjusting the total load u on said units, andmeans for simultaneous y maintaining balanced conditions between unitsirrespective of the total load. 7

15. In a system of control, the combinaq tion with a supply circuit, ofa plurality of from the supply circuit to the rst-named relay means.-

16. in a system of control, the combination with a supply circuit, of aplurality of induction motors energized therefrom to haul a common loadand each having a primary and a secondary winding, means forrespectively varying the resistance of the several secondary-windingcircuits, re-

lay means having elements opposingly energized from said supply circuitand said motors for controllingall of said resistancevarying' means tofix the total load upon said motors, and other relay means associatedwith the respective motors and eachcomprising elements opposinglyenergized irom certain circuits or the respective motors and fromcertain circuits oi the firstnamed relay means torseparately controllingthe resistance-varying means to halance the load hetween the severalmotors.

lln testimony whereof l have hereunto subscribed my name this '30thday'oi March,

'll UDULF HELLlldUNDr

